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Zimbabwe - Climate

Zimbabwe’s hunger crisis - the worst for more than a decade - is part of an unprecedented climate-driven disaster gripping southern Africa. Temperatures in the region are rising at more than twice the average global rate and ever more erratic rainy seasons are hitting the country’s subsistence farmers hard. The rainy season is increasingly unreliable and particularly affects subsistence farmers, as they grow corn, a crop that needs a lot of water, and many of them are still recovering from the drought caused by El Niño between 2014 and 2015. The World Food Programme (WFP) is rapidly expanding an already sizeable emergency operation in Zimbabwe where drought, flooding and macro-economic meltdown have plunged 7.7 million people – half the population – into severe hunger.

Zimbabwe's climate includes a warm, rainy season - the Southern Hemisphere summer - from November into March; a transitional period of diminishing rainfall extending into May; a cool and dry winter season from May to August; and a season that becomes increasinly warm and dry from August through October until both the progressive increase in daily temperatures and the annual drought are interrupted in November by the first rains of the succeeding wet season.

Mean annual rainfall varies considerably from one part of the ountry to another, but none receives great quantities drain, and as much as two-thirds of Zimbabwe receives less than 800 millimeters. Only parts of the eastern highlands get more than 1,200 millimeters of rain annually (in a few places as much as 1,800 millimeters), and substantial areas in the south and some in the northwest get only half that amount or a good deal less.

The level of rainfall is critically important. In half the country the effective rainfall is inadequate for dependable crop production, and rainfall may vary greatly from year to year. As a general rule, the lower the average rainfall, the lower is its dependability. Thus the lowveld areas -- subarid during the best of years -- suffer severely from wide variations in total rainfall, which occurs at frequent but irregular intervals.

Although not extreme, slopes in most areas are steep enough that much of the rain flows quickly to stream channels rather than soaking slowly into the subsoil or into subsurface aquifers. Some rainstorms are heavy, and much of their potential value is lost as the water rushes off croplands or grasslands into the rivers, possibly carrying topsoil away as well.

Moderately high altitude, low average cloud cover, and tropical sunshine result in a high rate of evaporation of surface water. Most of the country receives little significant rainfall between May and November, and many streams dry up entirely during this annual dry season. Some water is retained in vleis (natural storage pools lying on impermeable soil and rock strata). Many of these have been tapped by boreholes and wells and have become indispensable as water sources for people and animals during the long dry season.

Exacerbating Zimbabwe’s economic woes is the growing impact of climate change. The collapse of the commercial agricultural sector resulted in an over-reliance on small scale, rain-fed agriculture by farmers who often are not trained and frequently lack inputs. As Zimbabwe’s climate has become more erratic, farmers have found it harder to produce sufficient yields to meet demand. This has greatly contributed to the recurrent food insecurity as small-scale farmers, many of whom do not have access to irrigation, provide approximately 70 percent of Zimbabwe’s staple crops.

Zimbabwe is a country that prefers to grow maize despite the changing climate and increasing concerns regarding water scarcity. In Zimbabwe, maize is the primary food crop grown by small-holder farmers and is preferred over more drought-resistant crops such as millet and sorghum. This preference is reinforced by the government, which distributes maize rather than other seeds thereby frequently undermining free market incentives. Unfortunately, many Zimbabweans have yet to accept fully the realities of climate change and its implications.

With a pattern of crop failures happening in every three out of five years, food and nutrition security remains a persistent problem. Furthermore, climate change is likely to alter the patterns of water- and vector-borne diseases such as malaria, increase conflict around water access, as well as reduce access to clean water. The concern is that these new stresses will further erode coping strategies and pose additional threats to health and livelihoods.

In addition to food security, the tourism and industrial sectors are also experiencing the repercussions of climate change. As water scarcity affects livestock and humans, it also affects wildlife. This does not bode well for a sector dependent on a vibrant wildlife population. Already burdened by erratic utilities, industries also face climate-related challenges in the form of increased power shortages due to lower water levels in hydroelectric dams.

The El Niño/Southern Oscillation (ENSO) is a recurring pattern of interannual oscillations in both sea-surface temperature and sea-level atmospheric pressure in the tropical Pacific which shows strong correlations with climate patterns around the globe. Because of recent advances in ocean circulation modeling, it is now possible to predict ENSO events by as much as one year in advance. One region where rainfall is strongly influenced by ENSO is southern Africa, almost halfway around the globe from the Pacific Ocean.

Amid months of persistent heavy rains, Zimbabwe’s Meteorological Department reported that some areas of the country received their heaviest rainfall in 30 years during January 2012. Flooding in the region raised authorities’ concerns about the potential for the Zambezi River to overflow a dam, but the majority of the damage sustained in Zimbabwe was to crops.

As the country entered the second year of the 2014-2016 drought, estimates were that the Kariba dam, which both Zimbabwe and Zambia rely heavily on for electricity, only had sufficient water to supply electricity for six months.

Poor rains during the southern Africa monsoon (October 2015 through May 2016) led to extensive drought across Mozambique, Zambia, Zimbabwe, South Africa and southern Madagascar. The dismal rainy season destroyed crops, killed livestock, and even led to blackouts. The 2015-2016 rainy season ranks among the worst in at least the last 30 years for many areas. Rains since October have been below 80% of normal across a broad swath of southeastern Africa. Localized regions in central/southern Mozambique, Zimbabwe, and central South Africa received less than half their normal rainfall. Zimbabwe declared a state of disaster as more than a quarter of the population face food shortages. More than 16,000 cattle had died, while up to 75% of crops have been abandoned in the country’s driest areas.

Early planting in both El Niño and La Niña years could improve maize yields. For the El Niño years, this improvement was related to the timing of the critical pollination period for the crop. If drought stress occurs during pollination, it can cause fewer kernels to develop on the ears; early planting helped shift the pollination period to December before the January dry spell. In the case of the wetter La Niña years, the relative decrease in rainfall during January was not significant enough to reduce yields, and the advantage of early planting was due to improved nitrogen fertilizer use. Under the normal planting date, the high December rainfall in La Niña years can cause nitrogen to leach out of the soil before plant growth is strong enough to take it up. With earlier planting, most of the plant biomass accumulation occurs before this rainy period, and plants are able to "store" the nitrogen in their leaves before it is washed away.

There is concern that food insecurity will increase in southern Africa due to climate change. The temperature is projected to increase significantly in Zimbabwe by 2100 with no significant change in mean annual total rainfall. Fertilizer increased yield significantly under both baseline and future climates. The response of maize to mineral nitrogen decreased with progressing climate change, implying a decrease in the optimal fertilizer rate in the future. In the near future, improved crop and soil fertility management will remain important for enhanced maize yield. Towards the end of the 21st century, however, none of the farm management options can avoid large yield losses in southern Africa due to climate change.